# 1 Chapter 1 Overview of Programming and Problem Solving Dale/Weems/Headington Slides by Sylvia Sorkin, Community College of Baltimore County - Essex Campus.

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1 Chapter 1 Overview of Programming and Problem Solving Dale/Weems/Headington Slides by Sylvia Sorkin, Community College of Baltimore County - Essex Campus

2 Chapter 1 Topics l Computer Programming l Programming Life-Cycle Phases l Creating an Algorithm l Machine Language vs. High Level Languages l Compilation and Execution Processes l C++ History l Computer Components l Computing Profession Ethics l Problem-Solving Techniques

3 What is Computer Programming? It is the process of planning a sequence of steps (called instructions) for a computer to follow. STEP 1 STEP 2 STEP 3...

4 Programming Life Cycle Phases 1 Problem-Solving 2 Implementation 3 Maintenance

5 Problem-Solving Phase ANALYZE the problem and SPECIFY what the solution must do develop a GENERAL SOLUTION (ALGORITHM) to solve the problem VERIFY that your solution really solves the problem

6 Sample Problem A programmer needs an algorithm to determine an employee’s weekly wages. How would the calculations be done by hand?

7 One Employee’s Wages In one week an employee works 52 hours at the hourly pay rate of \$24.75. Assume a 40.0 hour normal work week and an overtime pay rate factor of 1.5 What are the employee’s wages? 40 x \$ 24.75 = \$ 990.00 12 x 1.5 x \$ 24.75 = \$ 445.50 ___________ \$ 1435.50

8 If hours are more than 40.0, then wages = (40.0 * payRate) + (hours - 40.0) * 1.5 *payRate otherwise, wages = hours * payRate Weekly Wages, in General RECALL EXAMPLE ( 40 x \$ 24.75 ) + ( 12 x 1.5 x \$ 24.75 ) = \$1435.50

9 An Algorithm is... a step-by-step procedure for solving a problem in a finite amount of time.

10 Algorithm to Determine an Employee’s Weekly Wages 1. Get the employee’s hourly payRate 2. Get the hours worked this week 3. Calculate this week’s regular wages 4. Calculate this week’s overtime wages (if any) 5. Add the regular wages to overtime wages (if any) to determine total wages for the week

11 What is a Programming Language? It is a language with strict grammar rules, symbols, and special words used to construct a computer program.

12 Implementation Phase: Program translating your algorithm into a programming language is called CODING with C++, you use Documentation -- your written comments Compiler -- translates your program into machine language Main Program -- may call subalgorithms

13 Implementation Phase: Test TESTING your program means running (executing) your program on the computer, to see if it produces correct results if it does not, then you must find out what is wrong with your program or algorithm and fix it--this is called debugging

14 Maintenance Phase USE and MODIFY the program to meet changing requirements or correct errors that show up in using it maintenance begins when your program is put into use and accounts for the majority of effort on most programs

15 Programming Life Cycle 1 Problem-Solving Phase Analysis and Specification General Solution ( Algorithm ) Verify 2 Implementation Phase Concrete Solution ( Program ) Test 3 Maintenance Phase Use Maintain

16 A Tempting Shortcut? GOAL THINKING CODE REVISE DEBUG TEST CODE Shortcut?

17 Memory Organization l two circuit states correspond to 0 and 1 l bit (short for binary digit) refers to a single 0 or 1. Bit patterns represent both the computer instructions and computer data l 1 byte = 8 bits l 1 KB = 1024 bytes l 1 MB = 1024 x 1024 = 1,048,576 bytes

18 How Many Possible Digits? l binary (base 2) numbers use 2 digits: JUST 0 and 1 l decimal (base 10) numbers use 10 digits: 0 THROUGH 9

19 Machine Language l is not portable l runs only on specific type of computer l is made up of binary-coded instructions (strings of 0s and 1s) is the language that can be directly used by the computer

20 High Level Languages l are portable l user writes program in language similar to natural language examples -- FORTRAN, COBOL, Pascal, Ada, Modula-2, C++, Java l most are standardized by ISO/ANSI to provide an official description of the language

21 Three C++ Program Stages other code from libraries, etc. other code from libraries, etc. written in machine language written in machine language written in machine language written in machine language written in C++ written in C++ via compilervia linker SOURCEOBJECT EXECUTABLE myprog.cppmyprog.objmyprog.exe

22 Java Programming Language l achieves portability by using both a compiler and an interpreter l first, a Java compiler translates a Java program into an intermediate bytecode--not machine language then, an interpreter program called the Java Virtual Machine (JVM) translates a single instruction in the bytecode program to machine language and immediately runs it, one at a time

23 Basic Control Structures l a sequence is a series of statements that execute one after another l selection (branch) is used to execute different statements depending on certain conditions l Looping (repetition) is used to repeat statements while certain conditions are met. l a subprogram is used to break the program into smaller units

24 SEQUENCE Statement...

25 SELECTION (branch) IF Condition THEN Statement1 ELSE Statement2 Statement1 Statement Statement2 Condition... True False

26 LOOP (repetition) Statement Condition... False True WHILE Condition DO Statement1

27 SUBPROGRAM (function) SUBPROGRAM1... SUBPROGRAM1 a meaningful collection of SEQUENCE, SELECTION, LOOP, SUBPROGRAM

28 Computer Components Arithmetic Logic Unit Control Unit Auxiliary Storage Device Memory Unit ( RAM & Registers ) Central Processing Unit ( CPU ) Input Device Output Device Peripherals

29 Memory Unit l is an ordered sequence of storage cells, each capable of holding a piece of information l each cell has its own unique address the information held can be input data, computed values, or your program instructions.

30 Central Processing Unit l has 2 components to execute program instructions n Arithmetic/Logic Unit performs arithmetic operations, and makes logical comparisons. n Control Unit controls the order in which your program instructions are executed.

31 Peripherals l are input, output, or auxiliary storage devices attached to a computer n Input Devices include keyboard and mouse. n Output Devices include printers, video display, LCD screens. n Auxiliary Storage Devices include disk drives, scanners, CD-ROM and DVD-ROM drives, modems, sound cards, speakers, and digital cameras.

32 Some C++ History l 1972 : Dennis Ritchie at Bell Labs designs C and 90% of UNIX is then written in C l Late 70’s : OOP becomes popular l Bjarne Stroustrup at Bell Labs adds features to C to form “C with Classes” l 1983 : Name C++ first used l 1998 : ISO/ANSI standardization of C++

33 Computing Profession Ethics l copy software only with permission from the copyright holder l give credit to another programmer by name whenever using his/her code l use computer resources only with permission l guard the privacy of confidential data l use software engineering principles to develop software free from errors

34 What is Computer Science? The Computing Curriculum 1991 (ACM/IEEE) l Algorithms and Data Structures l Architecture l Artificial Intelligence and Robotics l Database and Information Retrieval l Human-Computer Communication l Numerical and Symbolic Computation l Operating Systems l Programming Languages l Software Engineering l Social and Professional Context

35 Problem Solving Techniques l ASK QUESTIONS -- about the data, the process, the output, error conditions. l LOOK FOR FAMILIAR THINGS -- certain situations arise again and again. l SOLVE BY ANALOGY -- it may give you a place to start. l USE MEANS-ENDS ANALYSIS -- Determine the I/O and then work out the details.

36 More Problem Solving Techniques l DIVIDE AND CONQUER -- break up large problems into manageable units. l BUILDING-BLOCK APPPROACH -- can you solve small pieces of the problem? l MERGE SOLUTIONS -- instead of joining them end to end to avoid duplicate steps. l OVERCOME MENTAL BLOCK -- by rewriting the problem in your own words.

37 Company Payroll Case Study A small company needs an interactive program to figure its weekly payroll. The payroll clerk will input data for each employee, and each employee’s wages and data should be saved in a secondary file. Display the total wages for the week on the screen.

38 One Employee’s Wages In one week employee ID # 4587 works 52 hours at the hourly pay rate of \$24.75. Assume a 40.0 hour normal work week and an overtime pay rate factor of 1.5. What are the employee’s wages? 40 x \$ 24.75 = \$ 990.00 12 x 1.5 x \$ 24.75 = \$ 445.50 ___________ \$ 1435.50

39 Problem-Solving Phase What information will be used? INPUT DATA from outside the program FORMULA CONSTANTS used in program COMPUTED VALUE produced by program OUTPUT RESULTS written to file or screen by program

40 Problem-Solving Phase INPUT DATAFORMULA CONSTANTS OUTPUT RESULTS Employee ID Number Hourly payRate Hours worked Normal work hours ( 40.0 ) Overtime pay rate factor (1.5) Hourly payRate Hours worked Wages COMPUTED VALUE Wages

41 If hours are more than 40.0, then wages = (40.0 * payRate) + (hours - 40.0) * 1.5 *payRate otherwise, wages = hours * payRate Week’s Wages, in General RECALL EXAMPLE ( 40 x \$ 24.75 ) + ( 12 x 1.5 x \$ 24.75 ) = \$1435.50

42 Algorithm for Company Payroll Program l initialize total company payroll to 0.0 l repeat this process for each employee: 1. Get the employee’s ID empNum 2. Get the employee’s hourly payRate 3. Get the hours worked this week 4. Calculate this week’s wages 5. Add wages to total company payroll 6. Write empNum, payRate, hours, wages to file l write total company payroll on screen

43 // *************************************************** // Payroll program // This program computes each employee’s wages and // the total company payroll // *************************************************** #include // for keyboard/screen I/O #include // for file I/O using namespace std; void CalcPay ( float, float, float& ) ; const float MAX_HOURS = 40.0; // Maximum normal hours const float OVERTIME = 1.5; // Overtime pay factor C++ Program

44 C++ Code Continued int main( ) { float payRate; // Employee’s pay rate float hours;// Hours worked float wages; // Wages earned float total;// Total company payroll int empNum;// Employee ID number ofstream payFile;// Company payroll file payFile.open( “payfile.dat” );// Open file total = 0.0;// Initialize total

45 cout << “Enter employee number: “; // Prompt cin >> empNum; // Read ID number while ( empNum != 0 ) // While not done { cout << “Enter pay rate: “; cin >> payRate ; // Read pay rate cout << “Enter hours worked: “; cin >> hours ; // and hours worked CalcPay(payRate, hours, wages); // Compute wages total = total + wages; // Add to total payFile << empNum << payRate << hours << wages << endl; cout << “Enter employee number: “; cin >> empNum; // Read ID number } 45

46 cout << “Total payroll is “ << total << endl; return 0 ;// Successful completion } // *************************************************** void CalcPay ( /* in */ float payRate, /* in */ float hours, /* out */ float& wages ) // CalcPay computes wages from the employee’s pay rate // and the hours worked, taking overtime into account { if ( hours > MAX_HOURS ) wages = (MAX_HOURS * payRate ) + (hours - MAX_HOURS) * payRate * OVER_TIME; else wages = hours * payRate; } 46

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